Method of driving the gearing of an electronic timepiece and an electronic timepiece for implementing said method

ABSTRACT

An electronic timepiece comprises a device for indicating the time, which device includes a gear train and a time indicator controlled by said gear train, an electronic circuit which produces periodic signals of a predetermined frequency and an electromechanical transducer for driving said device, which transducer is controlled by the signals produced by the said circuit; the transducer incorporates a member which swings periodically and at the frequency of said signals, between two limiting positions in order, at least once during the course of two successive swings, to strike successively each tooth of a gear in the said gear train; means are provided in order to limit to a predetermined value the angular displacement of the gear as a consequence of each impact.

United States Patent METHOD OF DRIVING THE GEARING OF AN ELECTRONIC TIMEPIECE AND AN ELECTRONIC TIMEPIECE FOR IMPLEMENTING SAID METHOD 7 Claims, 9 Drawing Figs.

U.S. Cl

Int. Cl G04c 3/00 Field of Search 58/276, 23,

28, 28 A, 28 8,28 D, 116, I21

[56 1 References Cited UNITED STATES PATENTS 3,488,942 1/1970 Hougendobler 58/28 I Primary Examiner-Richard B. Wilkinson Assistant Examiner- Edith C. Simmons Attorney-Waters, Roditi, Schwartz & Nissen ABSTRACT: An electronic timepiece comprises a device for indicating the time, which device includes a gear train and a time indicator controlled by said gear train, an electronic circuit which produces periodic signals of a predetermined frequency and an electromechanical transducer for driving said device, which transducer is controlled by the signals produced by the said circuit; the transducer incorporates a member which swings periodically and at the frequency of said signals, between two limiting positions in order, at least once during the course of two successive swings, to strike successively each tooth of a gear in the said gear train; means are provided in order to limit to a predetermined value the angular displacement of the gear as a consequence of each impact.

PATENTED SEP] 4 I971 SHEET 1 OF 3 PATENTEDSEPMIB?! 3 04201 sum 2 or 3 PATENIEusEPmsn 3,604,201 sum 3 or 3 METHOD OF DRIVING THE GEARING OF AN ELECTRONIC TIMEPIECE AND. AN ELECTRONIC TIMEI'IECE FOR IMPLEMENTING SAID METHOD ln electronic timepieces the time base of which is constituted by a high-stability electronic oscillator, for example a crystal-controlled oscillator, theactual time display is often effected'bymechanical means- In situations where these timepieces must not only have particularly small dimensions in order to be carried by the user, and this is especially the case where electronic Wristwatches are concerned, the electromechanical transducer used in such watches has to satisfy a number of requirements which are specifically: Y 1

because of the smallamount of electrical energy which it. is possible to periodically supply to the transducer, the latter'must operate with a particularly high degree of efficiency; V

the reliability of operation of the transducer shouldbe relatively high'if errors in the time display produced: by said transducer, are not to cancel out the benefits derived from the use of a particularly accurate time base the transducer should be insensitive to external disturbances to which the timepiece may be subjected (shocks, magnetic fields, etc.).

The object of the present invention comprises a methodof driving the gear train of an electronic: timepiece, and. also an electronic timepiece: for implementing said method, by means of which it is possible to obtain a time display or. indication which satisfies the above conditions.

This method. is characterized in that each toothof. one of the gears of the gear train. successively receives an impact. and of that the angular displacement. in the gear, asaconsequence of each impact is limited to apredetermined value.

The electronic timepiece for implementing. said. method comprises a device for indicating the time,'whiclr device includes a gear train and a.time. indicator controlled by said. gear train, an electronic circuit producing: periodic. signals of a predetermined. frequency, and an electromechanical transducer for driving said device, which transducer is controlled by the signals produced. by said circuit, wherein saidtransducer incorporates a member which swings periodically, at the frequency of said signals, between: two limiting positions in order, at least onceduringthe course of two successive swings, to strike successively each tooth of a gear in the. gear train, and meansbeingprovided in orderto limitto apredetermined value the angular displacement of the gear asaconsequence of each impact;

The; attached drawing illustrates byway of example an. em.- bodiment of an electronic timepiece for implementing: the method formingthe object of the present invention:

FIG. 1 is a schematic view showing part of the-elements of said timepiece;

F lG. 2 is. an elevational view;

FIGS. 3, 4', 5 and6 are. detailed views illustrating various phases of operation of an electromechanicalatransducer of the kind fitted to the timepiece of; FIG. 1;;

FIGS. 7 and 8".are. explanatory diagrams.

H6. 9 is a. detailed. view of a. modification. of'one of thetimepiece elements.

The electronictimepiece-illustrated'in the.drawing:(FlGS; I and 2), comprises ahigh-precision oscillatorB,.forexamplea crystal-controlled oscillator: producing. a periodic highfrequency. signal, an electronicscaler D..- capable of dividing: the frequency of'saidisignal, for example down'toa valueot 1' Hz., and a circuit: ER: controlled by said. scal'erantt'designed to supply periodic pulses; to an electromechanical transducer in order to drive the second' wheel S of a-gear trainschematically represented by the. axis A. in order to controlthe hands H of the timepiece.

Thistransducer comprises ananchor-shaped movinggarmature 1' keyed" to a. spindle: 2. which ispitvotedat each: end in. jewels 3xands4. illustrated. schematically. in the drawing, said; spindle, carrying. two. hubs. 5' and. 6: for the attachment; or two spiral springs 7 and 8, and arm 9. These hubs are made, the first, of metal.and,.the second, of electrical-insulating material.

Secured to the armature 1" there isacoil 10 electrically connected to the spiral spring 7 'by'a connection 10a, soldered to the spindle 2, and by this-spindle, to the spiralspring- 8 by another connectionv 10b, said: plate extending in the plane of said armature between two U-shaped permanent magnets 11 and 12, which face one another withtheir open ends and are fixed to a. mountingplate which hasnot been shown.

Each magnet comprises two pole pieces Il a-and l-lb'( FIG. 1) made of ferromagnetic materialrhavinga very high coercive field strength, the pole pieces beingconnected to one another by ayoke 1100f. magnetizable material havinga low coercive field strength and high permeability:

The electromechanical transducer described is of the monostablekind and its armature l is biased'into the position. illustrated in FIG. 1, by thetwo spiral springs 7 and 8. As the illustration shows, the magnets 11' and 12 are positioned so that, talking into account. their dimensions and in particular the cross-sectional. area of their pole pieces, the turns of the coil are intersected by a maximum magnetic flux over the whole extent of the angular travel of the armature 1. This flux is, moreover, particularly strong in view of the fact that the magnets 11 and IZ are for the most part made-of material having a high magnetic energy and a high coercive field strength, and that the ratio of the length of the magnets to the width of the airgap within which the coil moves, is relatively large.

If an external field were superimposed upon the magnetic fieldv produced; by the: magnets IL and 12, this parasitic field would have no direct influence upon the driving of the armature l. and, therefore, on that of the gear train. of the timepiece. in order toexert a. disturbing effect on the coil 10,

' such a parasitic field. would have to be orientated in a predetemiinedadirectioniover one-half of the coil'width and in the-opposite direction: over the other half. In view of the; very small dimensions of the coil 10, amounting to some few in"- limeters in-diameter only, for example, it is virtually out of the question for any parasitic fieldtosatisfy the above condition.

The result is that the electromechanical transducer illustrated, is virtually completely insensitive to-the-efi'ect of magnetic. fields gccurring externally of the timepiece. However, this advantage isnot theonly one deriving from the above arrangement, aswillbetappreciated from the ensuing; description".

The spiral springsT and 8 are coiled in opposite directions and their external extremities, secured by conventional means to a balance cock (not shown) areconnected electrically, in the. case of the coil spring 7, to the-circuit ER, and in the case ofthe coil springr8, to earth, while theje wel bearingsjand 4 are assembled in insulating housings which have not been shown.

Because. the hubS to'which the-coil spring 7" is attached is made of metaland. is secured to the spindle Z-andthehub G isv made of. an insulating material: so: that there is no-electrical connection-between the-spiral'spring7 andthe spiral spring 8-, the pulses produced by thecircuitER are supplied tothe coil 10': through the spring 7 andthen': pass to earth through the spring8;

The arm 9 is designed to limit. the pivoting movement. of the armature by cooperation with'twostops Band 14 secured to thebridge on thebackingplatetnotshown), the stop filming the exit one, againstwhichithe arm 9-- abuts when-the armature L. is-i'n the rest condition, and. the stop 1 3 beingthe entry one, againstwhich thearm-strikeswhen ltis-swung in the direction F atthesame time. as the-armature 1: (H6. 1).

It is worthyot mention that. thespiral springs 7 and 8 are lightly loaded when the various moving elements of the transducerare in the position illustratedin FIG. 1 so that the arm 9 isappliedlightly against thestoplAa The drivingof the seconds wheelor gear Si of themovement is produced-exclusively by'the' alternate striking of the pallets 1aand. l'b' of the armature I against the'diffe rent teeth T5 of the wheel or: gear, in themanner now to be described in relationto FIGS. 1'. to 6.

This drive system is particularly relevant to the case where energy transmission is to be effected with maximum efficiency, and in particular where the amount of energy which can be supplied to the coil with each pulse from the circuit ER, is small. In other words, this method of driving by a single mechanical impulse, overcomes all the defects and drawbacks traditionally associated with drive systems which employ friction between components, Le. a quantity the value of which varies very widely and depends upon the condition of the surfaces involved and upon their changing characteristics with time and wear etc.

The transmission of energy by the striking of a driving element against a driven element, on the other hand, is determined exclusively by the geometrical dimensions of the moving parts and by the respective moving masses. As far as the losses involved in the transmission of energy by impact, are concerned, those skilled in the art will understand that these depend primarily upon the elastic properties of the materials directly involved in said transmission, and not upon the mechanical condition of the surfaces which come into contact with one another. In any case, if this surface condition was wrong after commencement of energy transmission by impact, it will improve very rapidly by consequence of repeated hammer blows between the surfaces involved, so that the energy transmission factor between drive element and driven element will be improved likewise.

It should be pointed out, nevertheless, that in the case of energy transmission by impact of a pivoting element, such as the armature 1, against the second rotary element, in the present instance the seconds wheel S, the efficiency with which said energy transmission takes place achieves a maximum only when the impact takes place in a direction which is tangential, at the point of impact, to the trajectory which is followed, after the impact, by that part of the said element which receives the impact. In the present instance, the second moving body is a toothed wheel and accordingly said trajectory will be circular.

However, when using a'toothed wheel, it is virtually out of the question to achieve this ideal condition, since each tooth preceding the one intended to be struck by the armature 1, or more particularly by the pallets la and 1b, presents an obstacle to said armature, and prevents the striking action taking place.

However, it can be shown that it is possible to obtain an energy efficiency equivalent to the ideal efficiency above defined, even if the impact does not take place tangentially to the circular trajectory followed by the different teeth of the seconds wheel but rather by the impact takes place normally to said trajectory, provided that the striker element, i.e. one or the other of the pallets with which the armature l is fitted, has a striker face which, like that part of the tooth which is involved in the impact, makes an angle of 45 with the tangent (taken at the point of impact of the former against the latter), to the circular trajectory followed by this part of the tooth after impact.

In the case of the transducer shown in FIG. 1, the position of the center of pivoting of the armature 1, the length of those arms of said armature which carry the pallets 1a and 1b, and the angular position of each pallet on its respective arm, have accordingly been chosen so that in the position of approach, each pallet is directed towards the center of pivoting of the wheel S when it hits said wheel. In addition, the end of the pallet is profiled in order to make an angle of 45 with the tangent to the circular trajectory followed by the different teeth of the wheel S.

The efficiency of the impulse driving system employed in respect of the gearing system of the timepiece, the impulse being applied tothe seconds wheel S (FIG. 1 and FIG. 2) by the pallets la and 11; of the transducer armature, can be defined in terms of the ratio of the kinetic energy stored by the gear train and by thedndicating hands of the timepiece, after the impact, to that-stored by the moving part of the electromechanical transducer prior to said impact, viz:

where 6 is the moment of inertia of the moving part of the transducer, that is to say the assembly comprising the spindle 2, the hubs 5 and 6, the coil springs 7 and 8, the armature 1 and the coil 10;

w is the angular velocity of said arrangement at the time of impact of the pallet in against a tooth of the wheel S;

0,, is moment of inertia of the gearing system and the indicator hands, with reference to the center of rotation .of the seconds wheel S;

10' is the angular velocity with which the wheel 8 rotates after having been hit by one of the pallets of the transducer.

If the impact of each pallet of the armature against the teeth of the wheel S takes place when said pallet is moving towards the center of rotation of the wheel, in the manner described, and if both the striker face of the pallets and that of the teeth of the wheel, are profiled in the manner described so that in both cases they are contained in a common plane inclined at 45 to the tangent (considered at the point of the teeth) to the circular trajectory of the zone of impact, then the efficiency equation defined above can equally well be written:

k is the recovery" coefficient which can have a value somewhere between 0 and l and is defined by the ratio of the velocity reached by an element of a given material after having fallen onto a fixed substrate likewise made of a given material but possibly of different nature, and the velocity which said same element had prior to hitting the substrate;

r, is the effective radius of the driving element, that is to say the distance separating the center of pivoting of the armature l, and the striker. face of one or other ofthe pallets;

r is the effective radius of the driven element, that is to say the distance separating the center of pivoting of the seconds wheel S and the impact-receiving face of each tooth;

0 and 00,, have the same significance as that hereinbefore defined.

For a given value of k, this efficiency is maximum when:

i. or

9R 1; 9B 7'A in order words when the moments of inertia of the moving element are in the ratio of the square of the respective effective radii of said components.

In addition, as in the present instance, velocities 10' and (a are relatively small and, taking into account the materials which can be used for the elements involved in the impact, it is possible to obtain a transmission coefficient k having a value quite close to l, and this indicates that the impact which takes placed is essentially elastic in nature.

It follows from the efficiency equation hereinbefore defined that, in the case where (L 1 9R a said efficiency can reach values close to unity so that energy transmission by impact is obviously of particular significance in the context of clock systems.

In order to ensure that on the occasion of impulse-energy transmission from one moving element to another, it shall be possible nevertheless to achieve friction between the first and second elements, in particular after the impact, it is essential that the velocity of the striker element after impact should become zero or negative in relation to the velocity which it had prior to impact.

In the case of the armature 1 described, and which approaches the wheel S by displacement of its pallets in the direction which is radially disposed in in relation to said wheel, it can be shown that the angular velocity w' of the assembly of spindle 2, hubs 5 and 6, spiral springs 7 and 8, armature 1 and coil 10, after the impact of a pallet la OR lb of the armature against one of the teeth of the wheel S, satisfies the relationship w mg 1 a TA)2 1 in which (u is the angular velocity of said same assembly before the impact, k, 0, 6 r, and r,, being the same quantities as hereinbefore defined.

If m' =0, then this relationship becomes i L 1 +-k 1 0R T32 from which we obtain pact, (w' =0), the efficiency of energy transmission is to reach the value If k has a value close to unity, said efficiency has the maximum value of unity hereinbefore referred to and the expres- Slot] 2.. L921 d liac fi becomes equal to unit in the manner hereinbefore described.

In practice, it is sometimes difficult -to achieve an electromechanical transducer and a gear train, in particular a seconds wheel S, which accurately satisfy the above conditions, either because the manufacture and assembly of the various elements cannot be effected with the necessary accuracy or because, in order to facilitate manufacture, one is forced to depart slightly from the theoretical values both as far as the slope which the tips of the pallets or the flanks of the teeth of the seconds wheel, should have, or as far as the movement of inertia 0 or 0,, is concerned.

The efficiency of the overall timepiece mechanism depends also upon the method by which the electrical energy of the pulses periodically supplied to the transducer R, is converted into mechanical energy to drive the armature.

The efficiency of an electrodynamic transducer is proper tional, on the one hand, to the mean velocity of displacement of the armature l and all the moving parts associated therewith, i.e. the drive coil and, on the other hand, and for a given supply voltage, to the mean flux across the coil 10 during the drive phase. It will be understood by those skilled in the art that it is, under these circumstances, to arrange for the means velocity of the armature of the transducer to be very high and for the magnetic field produced by the magnets 11 and 12 to have a particularly high value. It is precisely because it is desirable to enable the armature l to be accelerated very rapidly, that is has been chosen to make the coil 10 mobile and the magnets 11 and 12 fixed. In addition, despite the small size of the transducer, the magnetic flux produced is particularly strong, these magnets being made of a ferromagnetic material having high coercive field strengths. In addition, the magnets have a relatively large volume in relation to the volume of the airgap between them, the coil 10 moving through said airgap in the manner described.

In the rest condition, the moving elements of the transducer thus occupy the position shown in FIGS. 1 and 2, abutting against the stop 14 through the medium of the arm 9 under the action of the torque exerted by the two spiral springs 7 and 8. This torque will be made sufficiently large to ensure that even the most intense disturbing accelerations-at which a watch can be submitted, in normal use conditions, could be not sufficient to tilt the armature 1 in such a mann'erthatthe pallet la could strike against a tooth of the wheels.

If, on the other hand, the moving elements of the transducer are in fact moving, and a disturbing acceleration takes place, the effect of this acceleration will vary depending upon whether it is the direction F or in the opposite direction. In the first instance, the disturbing acceleration will sustain the movement of the armature l which is being driven by the occurrence of a pulse in the coil 10, and this does not constitute any nuisance; in the second case, the acceleration will be opposed to the movement and, if required, may inhibit contact between the pallet 1a and a tooth of the wheel S. In order to render the operation of the transducer as far as possible insensitive to external shocks, it is therefore essential to arrange that the kinetic energy imparted to the moving elements of said transducer by the torque resulting from the combined action of the coil 10 and the magnets 11 and 12, is as large as possible, ensuring that the mean velocity of displacement of these elements is high. Of course, since the time of displacement of the moving elements in each direction of swing is very short, the period of time for which such a disturbing acceleration could be effective, will be very short indeed.

When the electromechanical transducer is in the rest condition, the armature l occupies the position shown in FIGS. 1 to 3: As FIG. 3'illust'rates in detail, the pallet lb of the armature is then engaged between two teeth of the wheel 5 and locks the latter against angular movement and accordingly the remainder of the gear system of the timepiece too.

As soon as a pulse arrives from the circuit ER in the coil 10, the armature is accelerated in the direction F until the pallet la hits the striker face b of a tooth d of the wheel S (FIG. 4), with its own striker face a. The result is that the major parts of the kinetic energy stored in the moving elements of the transducer is transmitted to the wheel 8 which then displaces in the direction F until the tooth 11,. which was initially struck, clears the pallet la. The position of the latter pallet at this instant is determined by contact between the arm 9 (FIG. 1) and the stop 13.

The spiral springs 7 and 8 are fully tensioned and exert a returning force on the armature 1 in the direction F so that said armature is swung back towards the left (considered in the drawing) until the pallet lb clears the tooth 11,, the wheel S then experiencing an impact which transfer a new quantity of kinetic energy to it, moving it in the direction F until the pallet lb enters the space defined between said tooth d and the following tooth 11,. The arm 9 which limits the movement, then hits the stop 14. Y

The above process then starts all over again with the at the transducer R of a new electrical pulse, and so on.

As FIGS. 5 and 6 show, the first impact on the tooth d, of the wheel S, simply advances said wheel by a distance corresponding substantially to the length of a tooth pitch, reduced by the width of the pallet la (FIGS. 4 and 5), while the second impact, against the tooth d causes the wheel to advance by a value equivalent to the width of the pallet 1b (FIGS. 6 and 3) so that overall, the wheel S is moved a distance equivalents to a tooth pitch with each electrical pulse received by the electromechanical transducer.

It is a similar situation which is depicted in FIG. 7, the latter illustrating, as a function of time, how the angular velocity (a of the armature l varies each time the electromechanical transducer receives a pulse 1', and how the angular displacement 1 of the wheel S due to the impulse which it periodically receives, takes place.

In particular, it will be observed that the velocity w rises to a maximum w, as long as the pulse lasts, dropping rapidly to zero at the instant I, at which the impact of the pallet 1a occurs, after which instant the wheel S commences to move, the armature and the wheel then occupying the position shown in FIG. 4. The displacement of the wheel S takes place over an angular interval il up' to the time t that is to say up to the arrival time at which the tooth d, following the one just hit, comes into'contact with the pallet In of the armature 1 (FIG. 5), the latter commencing to move in the direction F under the action of the spiral springs 7 and 8. The velocity of said armature, which is reduced substantially to zero between the times t, and t and which has risen to a value m drops off suddenly down to a value at the instant i at which the pallet lb of the armature hits the tooth d of the wheel S (FIG. 6). After this instant I the wheel S commences to move through an angular interval equivalent to I I the factor D corresponding to a tooth pitch, until the tooth d, of the wheel clears the pallet 1b of the armature (instant 1,) this pallet having penetrated into the space separating the teeth d and d As FIG. 7 shows, the angular velocity m of the armature l which had dropped to a), at the time of impact, has increased slightly thereafter to a value 0),, only to drop to zero at the instant which corresponds to the time at which the armature reverts to the position shown in FIG. 1, in contact with the stop 14 through its arm 9.

The number of teeth on the wheel S is of the order of 60 and the frequency of the pulses coming from the circuit ER is of the order of 1 Hz., so that the seconds hand of the timepiece, which is associated with this wheel, indicates the advance in time of I second with each swing of the armature l, i.e. with each pulse.

The general arrangement of the armature l, the pallets la and lb, and the toothing of the wheel S, is such that said wheel is never free to move in the angular sense during that part of the swinging movement of the armature which precedes and follows each impulse or impact, the pallets of the armature being alternately in engagement with the toothing.

As hereinbefore described, the electromechanical transducer of the timepiece is of the monostable kind so that the driving of the armature l is effected by pulses of the same polarity. Although this method of driving means that said pulses can be produced in a simple manner, since they can be obtained from the output of a binary sealer for example, it nevertheless gives rise to a mechanical drawback for the following reasons: After the first impact between armature and wheel, the armature loses speed, in fact it may even come to a halt, and is then simply subject to the restoring couple developed by the spiral springs 7 and 8. 0n the other hand, the toothed wheel has received virtually all the momentum energy of the armature so that it is displacing rapidly. The result is that the next tooth of the wheel, i.e. the one following the one just struck by the entry pallet of the armature, may hit said pallet before the latter has been able to clear the circular trajectory described by the tips of the teeth (see FIG. 5).

It goes without saying that this kind of impact must be avoided, since it in no way contributes to the correct operation of the timepiece.

Moreover, this kind of impact can, under certain circumstances and by virtue of a rebound effect on the part of the wheel S, return the wheel to its initial position so that the timepiece is slow.

It is possible to overcome this drawback by adding to the circuit ER a differentiating circuit of the RC kind, which converts each rectangular waveform pulse i (FIG. 8), into a train of two pulses I and I: of mutually opposite polarity.

For this method of driving, the electromechanical transducer of the timepiece described, remains exactly the same as illustrated in FIGS. land 2 as far as its general structure is concerned, although it will be understood that from the electromechanical point of view it will be modified as compared with the system employed in the case where strictly rectangular waveform pulses are used, as for example the pulses i (FIG. 8).

In other words, although the acceleration of the armature 1 under the effect of the pulse l the latter for example of positive polarity, takes place normally, the situation is slightly different as far as the phase of return of the armature to the rest position, after the impact of the pallet In of the tooth d, (FIG. 4) under the action of the spiral springs 7 and 8, is concerned.

Specifically, the annature 1, which is virtually at a standstill after the impact, is then not only driven backwards by the spiral springs but also by the effect of the negative polarity pulse 1,. The result is that the armature is accelerated back into the rest position much faster than it would be under the sole effect of the spiral springs 7 and 8, and that as a consequence the pallet la can be withdrawn from the gap between the tooth d, and the tooth a, before the latter hits it, so there is no longer any loss of energy from the wheel S of the kind which would otherwise occur if there was contact between it and the armature 1. Thus, by appropriately dimensioning the moving elements of the transducer, including the spiral springs, the gearing of the timepiece and the differentiating circuit associated with the circuit ER, it is possible to arrange that the sole contacts which take place between the pallets la and lb and the teeth of the wheel S, are ones during which energy is transferred to said wheel by impact with the pallets, said transmission thus being effected with a particularly high efficiency.

It is likewise possible, in accordance with a variant embodiment illustrated in FIG. 9, to prevent the blocking of the seconds wheel, S by contact between the tooth d and the pallet la after the striking of the preceding tooth, by cutting the end of said pallet in such a manner as to produce a face e which makes an angle of with the face a already described, said face e being designed to undergo contact with the tip of the tooth d when the wheel S is moving in the direction F under the effect of the impact which has previously taken place with its tooth d,. This recovery of energy by the armature 1 from the wheel S is sufficient to accelerate the former rapidly back into its stable position. In the case of this variant embodiment, the drive pulses may take a rectangular form in the manner of the pulses i shown in the diagram V of FIG. 7.

A similar effect can equally well be achieved by employing a transducer similar to the one shown in FIGS. 1 and 2, in particular as far as the general form of its elements (notably the pallet la and lb and the teeth of the wheel S) are concerned, and also as far as the method of supply of periodic pulses i is concerned, by dimensioning the moving elements of the transducer and the gearing arrangement in order that the velocity w of the armature after impact is not zero but slightly negative in relation to the velocity u which it has prior to impact.

Returning to the expression hereinbefore referred to and defining w' as a function of m k, 0, 6 r and r,,, we can then write l z i 1 +1... LAY 0R. 's

from which we obtain so that if, for a given k value, the various geometric quantities 0 0, r,,, r are chosen in order to satisfy this equation, the armature I will rebound slightly after impact between the pallet la and the tooth d, of the wheel S, and this will increase the angular velocity given to said armature by the action of the spiral springs 7 and 8, in its movement in direction F In addition to the qualities which any electromechanical transducer should exhibit, and which have been referred to hereinbefore, the transducer used in the timepiece described exhibits the following advantages:

the positioning of the moving elements of the electromechanical transducer takes places in such fashion that said elements are maintained in a single stable state so that the method by which the transducer is electrically driven becomes particularly simple;

the driving of the gear train is in a step-by-step manner at a very low frequency (1 Hz. for example), and this makes it possible to design a mechanical section of the transducer to have dimensions and an accuracy which are, to an order of magnitude, compatible with those of conventional timepieces.

Finally, although the present description and the attached drawings have simply dealt with the case of the impulse-driving of the gearing of a timepiece by action upon the seconds wheel of said gearing, saying it would equally be possible to achieve this same drive function by impulse operation of another moving part of said gearing, it being understood that drive pulses of an appropriate frequency would have to be provided.

I claim:

1. An electronic timepiece, comprising a device for indicating the time, which device includes a gear train and a time indicator controlled by said gear train, an electronic circuit which produces periodic signals of a predetermined frequency, and an electromechanical transducer for driving said device, which transducer is controlled by the signals produced by the said circuit, wherein said transducer incorporates a member which swings periodically and at the frequency of said signals, between two limiting positions in order, at least once during the course of two successive swings,.to strike successively each tooth of a gear in the gear train, means for limiting to a predetermined value the angular displacement of the gear as a consequence of each impact, said member comprises elements, one of said elements striking the teeth of said gear and following a radial trajectory in relation to said gear at the point of impact, the impact-applying surface of said element and the impact receiving of each tooth of the gear at the time of impact, being contained in a common plane making an angle substantially 45 with a tangent at the center of the zone of impact of the member which strikes against the tooth to the circular trajectory followed by the center of the impact zone on the tooth during the rotary motion imparted to the gear by the impact.

2. A timepiece as claimed in claim 1, wherein said member and said time-indicating device are so dimensioned that the moment of inertia of the member and that of the moving parts of said device (0 with reference to the center of rotation of the gear, the distance (r separating the zone of impact of said member from its pivot, and the distance (r separating the zone of impact on each tooth of said gear from its center of rotation, substantially satisfy the equation in which k is the coefficient of restoration at impact.

v 3. A timepiece as claimed in claim 2, wherein the electromechanical transducer is of the monostable kind; and wherein said member comprises an anchor-shaped armature supporting a pair of pallets each of which acts as a hammer for applying an impact to the teeth of said gear and hits each tooth of said gear in succession, firstly when said armature is moving into its unstable limiting position and secondly when as it returns to its stable limiting position, the extremity of each pallet being profiled to form said surface of said member which strikes the teeth of the gear, and wherein at least one spiral spring is associated with the armature to return said armature into its stable position each time it has moved away therefrom.

4. A timepiece as claimed in claim 3, wherein said limiting means are constituted, by each pallet of the armature and by the space separating the teeth of the gear, the pallets penetrating into said space when the armature is in its stable limiting position and when said armature is in its second, unstable limiting position.

5. A timepiece as claimed in claim 4, wherein said member and said time-indicating device are so dimensioned that, the moment of inertia (0) of said member and that (0,, of the moving parts of said device with reference to the center of rotation of the gear which is subjected to the impact and the distance (r,, separating the point of impact of said member from its pivot, and the distance (r separating the center of the zone of impact on each tooth of the gear from the center of rotation thereof, satisfy the relationship 6. A timepiece as claimed in claim 4, wherein said pallet of the armature which strikes the toothing of the gear when said device is moving into its unstable limiting position, has a second face adjacent the impact applying surface of said element, which second face is substantially perpendicular to the plane of said applying surface.

7. A timepiece as claimed in claim 4, comprising an RC differentiating circuit connected between the electronic circuit and the electromechanical transducer, said differentiating circuit producing a train of two pulses having mutually opposite polarities, in respect of each periodic signal received by the electronic circuit. 

1. An electronic timepiece, comprising a device for indicating the time, which device includes a gear train and a time indicator controlled by said gear train, an electronic circuit which produces periodic signals of a predetermined frequency, and an electromechanical transducer for driving said device, which transducer is controlled by the signals produced by the said circuit, wherein said transducer incorporates a member which swings periodically and at the frequency of said signals, between two limiting positions in order, at least once during the course of two successive swings, to strike successively each tooth of a gear in the gear train, means for limiting to a predetermined value the angular displacement of the gear as a consequence of each impact, said member comprises elements, one of said elements striking the teeth of said gear and following a radial trajectory in relation to said gear at the point of impact, the impactapplying surface of said element and the impact receiving of each tooth of the gear at the time of impact, being contained in a common plane making an angle substantially 45* with a tangent at the center of the zone of impact of the member which strikes against the tooth to the circular trajEctory followed by the center of the impact zone on the tooth during the rotary motion imparted to the gear by the impact.
 2. A timepiece as claimed in claim 1, wherein said member and said time-indicating device are so dimensioned that the moment of inertia ( theta ) of the member and that of the moving parts of said device ( theta R), with reference to the center of rotation of the gear, the distance (ra ) separating the zone of impact of said member from its pivot, and the distance (rA ) separating the zone of impact on each tooth of said gear from its center of rotation, substantially satisfy the equation in which k is the coefficient of restoration at impact.
 3. A timepiece as claimed in claim 2, wherein the electromechanical transducer is of the monostable kind; and wherein said member comprises an anchor-shaped armature supporting a pair of pallets each of which acts as a hammer for applying an impact to the teeth of said gear and hits each tooth of said gear in succession, firstly when said armature is moving into its unstable limiting position, and secondly when as it returns to its stable limiting position, the extremity of each pallet being profiled to form said surface of said member which strikes the teeth of the gear, and wherein at least one spiral spring is associated with the armature to return said armature into its stable position each time it has moved away therefrom.
 4. A timepiece as claimed in claim 3, wherein said limiting means are constituted, by each pallet of the armature and by the space separating the teeth of the gear, the pallets penetrating into said space when the armature is in its stable limiting position and when said armature is in its second, unstable limiting position.
 5. A timepiece as claimed in claim 4, wherein said member and said time-indicating device are so dimensioned that, the moment of inertia ( theta ) of said member and that ( theta R ) of the moving parts of said device with reference to the center of rotation of the gear which is subjected to the impact and the distance (ra ) separating the point of impact of said member from its pivot, and the distance (rA ) separating the center of the zone of impact on each tooth of the gear from the center of rotation thereof, satisfy the relationship
 6. A timepiece as claimed in claim 4, wherein said pallet of the armature which strikes the toothing of the gear when said device is moving into its unstable limiting position, has a second face adjacent the impact applying surface of said element, which second face is substantially perpendicular to the plane of said applying surface.
 7. A timepiece as claimed in claim 4, comprising an RC differentiating circuit connected between the electronic circuit and the electromechanical transducer, said differentiating circuit producing a train of two pulses having mutually opposite polarities, in respect of each periodic signal received by the electronic circuit. 